1. Field of the Invention
The present invention relates to a structure for cooling a lamp that is used for a projection display apparatus, and more particularly, to a structure for cooling a high-power lamp.
2. Description of the Related Art
With the reduction in size and improvement in performance of projection display apparatuses, which has been brought about through a rapid advance in liquid crystal technologies and DLP (Digital Light Processing; trademark) technologies, projection display apparatuses for projecting an image have been used in wider fields. The projection display apparatus is drawing attention as a front projector, which is a large projection display apparatus that is replacing conventional home-use television sets. The projection display apparatus has also been used for showing movies, as a digital cinema (DLP cinema) projector, because of the high resolution panel that enables the apparatus to project high-resolution images at full size.
Conventionally, a movie is displayed by projecting images stored in a video film onto a very large screen, for example, in a theater. Digital cinema is common to the conventional cinema in that images are projected and displayed on a very large screen. However, the digital cinema is different from the conventional cinema in that digital data are used for projection, instead of a film, and are projected onto a screen by a projection display apparatus, or by a digital cinema projector. The digital cinema largely differs from a front projector, which is used, for example, in a classroom or a conference room, in size, brightness, and reliability.
For example, a front projector typically employs an ultra-high pressure mercury lamp of approximately 300 W at the highest as a light source, whereas, a digital cinema projector requires a xenon lamp of 2 kW to 6 kW. Therefore, the amount of heat that is generated by a lamp and the size of a lamp, as well as danger, are incomparably larger than that of a front projector, and the entire size and the total weight of the apparatus also incomparably larger than that of a front projector.
Main parts of a xenon lamp that require cooling are a cathode, an anode, and a bulb. Conventionally, a fan is arranged on the backside of the cathode, and cooling air is supplied by the fan in a straight line along an optical axis of the lamp. As a result, the cathode, the bulb, and the anode are sequentially cooled. When the lamp is replaced, the xenon lamp itself is replaced with a new one. Japanese Patent Laid-Open Publication No. 2005-31549 discloses a structure for cooling a lamp, which has a heat sink for a xenon lamp, and two fans for cooling the xenon lamp.
According to another related art, a lamp house is provided to hold a xenon lamp therein, and the lamp is replaced by replacing the lamp house. The lamp is cooled by cooling air that is supplied toward the cathode, the anode, and the bulb from a direction perpendicular to the optical axis of the lamp.
Referring to FIG. 1A, a lamp, not shown, is arranged in a lamp house such that an anode, a bulb, and a cathode of the lamp are aligned in this order in the top-to-bottom direction of the figure. Light is emitted to the outside through explosion-proof glass 125. A pair of sirocco fans 140 are provided on the bottom surface of lamp house 121 at the locations that correspond to the anode and cathode, respectively. Referring to FIG. 1B, cooling air is supplied into lamp house 121 via each intake port along the direction indicated by the arrows, and after cooling the lamp, is exhausted to the outside via exhaust duct 123, which is provided outside lamp house 121, along the direction indicated by the arrow.
In related art, there are some problems to be addressed. The first problem is how safety can be ensured when replacing a xenon lamp. The second problem is efficiency for cooling a xenon lamp. And the third problem is the size of a lamp house or the size of a projection display apparatus.
Each portion of a lamp can be cooled by supplying cooling air straight along an optical axis of the lamp. However, an anode, which is located downstream of a double reflector for a bulb, cannot be sufficiently cooled according to this method because the double reflector has a large diameter. Also, because a xenon lamp needs to be replaced as a whole and because it is mounted in a congested area in the main body of a projection display apparatus, additional effort is required to replace the xenon lamp. Therefore, it is not recommended that a user replace a xenon lamp by himself, and replacement work is only performed by those who have training and are qualified by a certifying authority. Therefore, there are needs for improvement of safety and easy replacement.
In related art concerning lamp houses, exhaust duct 123 is connected to lamp house 121 at the outside of lamp house 121, as illustrated in FIGS. 1A, 1B. Cooling air that enters lamp house 121 from the lower side of lamp thereof remains stagnant in lamp house 121 after it cools the corresponding electrodes, and is not efficiently exhausted. Thus, there is a limitation for improving cooling efficiency. Further, since the cooling air is supplied to the cathode and the anode along a direction that is perpendicular to the optical axis of the lamp, a sufficient amount of cooling air cannot be supplied to the bulb, which makes it particularly difficult to efficiently cool the bulb and to properly control the cooling (temperature setting). Also, the structure in which the exhaust duct is arranged outside the lamp house causes an additional increase in the outer dimensions of a projection display apparatus.
When a xenon lamp is replaced, a lamp house that houses a xenon lamp needs to be removed from the projection display apparatus because the xenon lamp is integrated with the lamp house. This operation requires opening a side panel of the lamp house, and therefore, needs a larger number of steps. Further, care must be taken to ensure safety during replacement of a lamp, because the size of the opening on the side of the lamp house is limited.